In the aeronautical industry, it is generally known to reinforce fuselage skin panels with several types of stringers: such as T, U, J and omega-shaped stringers, in order to withstand the high loads that an aircraft has to withstand during flight, take offs, and landings.
FIGS. 1A and 1B show two different types of stringers joined to a skin panel. In the case of FIG. 1A, a “T-shaped” stringer (2) is joined to a skin panel (1), and in the case of FIG. 1B, an omega-shaped stringer (2) is joined to a skin panel (1). These two elements, panel and stringer, are joined either by co-curing both elements together, by co-bonding one element to the other, or by secondary bonding both elements.
In can be observed in FIG. 1A, that the cavity defined between the stringer (2) and the skin panel (1), is filled with a third element usually called rowing or filler (3), which is integrated in the structure during its manufacture. In the case of the omega stringer of FIG. 2B, two rowings (3) are used to fill the cavity defined between the stringer (2) and the skin panel (1).
The main purpose of these rowings is to fill the cavities generated during the manufacturing process to facilitate consolidation of the carbon fiber layers the stringer and panel during the curing process. Furthermore, these rowings serve to minimize the formation of cracks, and to minimize damages in vacuum bags during the consolidation process.
Manufacturing of these rowing is both time-consuming and expensive, because they have to be produced in large quantities, and there are no machines especially adapted for their manufacture is an automated manner. This means that currently, the manufacture of these rowing involves many manual steps, which is not only slow but also originate quality problems, since the repetitiveness of the desired shape of the rowing cannot be assured.
FIGS. 2A-2E shows various illustrations of a conventional process for producing these rowings. First, a sheet of carbon fiber is manually cut (FIG. 2A) to form strips of carbon fiber, which are then manually rolled-up one by one to form a rolls of carbon fiber (FIG. 2B). A set of rolls are then placed individually in a conforming tool (FIG. 2B), provided for that purpose with a plurality of channels or grooves to accommodate each roll.
This conforming tool is part of a press, which is used to conform the rolls by the simultaneous disclosure of pressure and heat (FIGS. 2D and 2E). The disclosure of pressure may be carried out by generating vacuum inside a membrane inside which the rowing are placed.
As it can be appreciated clearly from FIGS. 2A-2E, the current process for producing these rowings is slow because involves several manual operations, and the quality of the finished component depends on the skills of a human operator.